Over the weekend a photo from Frontier offices, circa October 2014 surfaced. The photo was of a whiteboard concerning audio development, but posted on the corner of the whiteboard was a series of ship concept arts and ship renders.
This is where it gets interesting
From the concept art, I can identify all but the smallest ships. Interestingly the ships are all grouped by manufacturer.
The renders are all top-down. This gives us a clear indication of size, or at least the size Frontier planned.
Some of the ships are in their "early" form. The Imperial Clipper was still known as the Imperial Trader and was larger than the final Clipper became. The Courier was in the early concept stage and as we know changed a great deal in implementation.
As you can see the Panther and Beluga top-downs show they are both longer than the Anaconda and Corvette. We are fairly certain that large pad is the hard limit of ship sizes and the pad would appear to be approximately 200m x 120m. The Beluga therefore is likely to be the same size as the Imperial Cutter and the Panther is that much larger, so probably very close to the maximum 200m long. That would make the Panther a pretty massive ship!
With Horizons 2.2 "Guardians" we are going to get passenger missions, so it follows that the most likely time for the Dolphin and Beluga Liner to sail into the game is in this version.
When will we see the Panther Clipper? Well 2.1 would be a nice surprise, but my bet is the ship and maybe some others of the same size class, are being held back for something special in 2.4. Currently passing cargo is a matter of eject-n-scoop between two ships, but with advent of super-heavy traders in the game maybe we'll see a ship-to-ship docking mechanism added for cargo (and passenger?) transfer direct.
This would allow for player-to-player cargo transfer and ships as large as the Panther could visit tiny outposts like Hutton Orbital and be unloaded by a group of Type 6 transports. It would also allow for the transfer of passengers to ships. Maybe you can take some guests to that wedding barge?